Light emitting diode with high melanopic spectral content

ABSTRACT

This specification discloses lighting device the includes a combination of a royal-blue and blue pump LEDs with a mixture of phosphors to provide light with a high melanopic content and maximize an m/p ratio while maintaining high color fidelity, and a tunable lighting system including the lighting device.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional application No.62/845,474, filed May 9, 2019, which is incorporated by reference in itsentirety.

FIELD OF THE INVENTION

The disclosure relates generally to lighting devices, and in particularto lighting devices having a high melanopic spectral content, and totunable lighting systems using such lighting devices.

BACKGROUND

Semiconductor light emitting diodes and laser diodes (collectivelyreferred to herein as “LEDs”) are among the most efficient light sourcescurrently available. The emission spectrum of an LED typically exhibitsa single narrow peak at a wavelength determined by the structure of thedevice and by the composition of the semiconductor materials from whichit is constructed. By suitable choice of device structure and materialsystem, LEDs may be designed to operate at ultraviolet, visible, orinfrared wavelengths.

LEDs may be combined with one or more wavelength converting materials(generally referred to herein as “phosphors”) that absorb light emittedby the LED and in response emit light of a longer wavelength. For suchphosphor-converted LEDs (“pcLEDs”), the fraction of the light emitted bythe LED that is absorbed by the phosphors depends on the amount ofphosphor material in the optical path of the light emitted by the LED,for example on the concentration of phosphor material in a phosphorlayer disposed on or around the LED and the thickness of the layer.

Phosphor-converted LEDs may be designed so that all of the light emittedby the LED is absorbed by one or more phosphors, in which case theemission from the pcLED is entirely from the phosphors. In such casesthe phosphor may be selected, for example, to emit light in a narrowspectral region that is not efficiently generated directly by an LED.

Alternatively, pcLEDs may be designed so that only a portion of thelight emitted by the LED is absorbed by the phosphors, in which case theemission from the pcLED is a mixture of light emitted by the LED andlight emitted by the phosphors.

SUMMARY

In one aspect, a lighting device as disclosed herein may include a lightsource, the light source including a royal-blue light source configuredto emit a royal-blue light with a peak wavelength range of 435-460 nmand a blue light source configured to emit light with a peak wavelengthrange of 470-496 nm; a wavelength converting structure disposed in apath of the royal-blue light and the blue light, the wavelengthconverting structure including: a green phosphor, the green phosphorconfigured to absorb a first portion of at least one of the royal-bluelight and the blue light, and to down-convert the first portion to greenlight; and a red phosphor configured to absorb at least one of a secondportion of at least one of the royal-blue light and the blue light and aportion of the green light and to down-convert the at least one of thesecond portion and the portion of the green light to red light; thewavelength converting structure configured to emit a second light, thesecond light including the green light, the red light, an unconvertedportion of the royal-blue light, and an unconverted portion of the bluelight.

The lighting device may include a second blue light source configured toemit light with a peak wavelength range of 470-496 nm.

A ratio of radiant flux of blue light having a wavelength range of 465to 495 nm to radiant flux of royal-blue light having a wavelength in therange of 435 to 465 nm in the second light of the lighting device may bebetween 0.9 and 2.0.

The royal-blue light source of the lighting device may be a royal-blueLED and the blue light source of the lighting device may be a blue LED.

The lighting device may additionally include a lead frame cup package,the royal-blue LED and blue LED may be both mounted inside the leadframe cup package, the wavelength converting structure may be disposedover the royal-blue LED and blue LED within the lead frame cup package.The royal-blue LED and the blue LED in the lead frame cup package may beelectrically connected in series.

An m/p ratio of the second light in the lighting device may be greaterthan an m/p ratio of the CIE daylight illuminant at a corresponding CCTvalue.

The second light may have a maximum spectral power density between 447nm 447 and 531 nm. The second light may have a maximum spectral powerdensity between 465 and 515 nm.

A CCT value of the second light may be 4000K or greater, and a colorrendering index of the second light may have an Ra value greater than80.

In another aspect, a tunable lighting system as disclosed herein mayinclude a first lighting device configured to emit a first light, thefirst light having a first m/p ratio; and a second lighting deviceconfigured to emit a second light, the second light having a second m/pratio that is smaller than the first m/p ratio, the tunable lightingsystem being configured to emit a third light, the third light includingat least one of the first light, the second light, or a combination ofthe first light and the second light, the first lighting device mayinclude: a light source, the light source including a royal-blue lightsource configured to emit a royal-blue light with a peak wavelengthrange of 435-460 nm and a blue light source configured to emit lightwith a peak wavelength range of 470-496 nm; a wavelength convertingstructure disposed in a path of the royal-blue light and the blue light,the wavelength converting structure including: a green phosphor, thegreen phosphor configured to absorb a first portion of at least one ofthe royal-blue light and the blue light, and to down-convert the firstportion to green light; and a red phosphor configured to absorb at leastone of a second portion of at least one of the royal-blue light and theblue light and a portion of the green light, and to down-convert the atleast one of the second portion and the portion of the green light tored light; the wavelength converting structure being configured to emitthe first light, the first light including the green light, the redlight, an unconverted portion of the royal-blue light, and anunconverted portion of the blue light.

In the tunable lighting system, the royal-blue light source may be aroyal-blue LED, the blue light source may be a blue LED, and the secondlighting device may be violet pumped LED.

In the tunable lighting system, the first lighting device may furtherinclude a lead frame cup package, the royal-blue LED and blue LED mayboth be mounted inside the lead frame cup package, and the wavelengthconverting structure may be disposed over the royal-blue LED and blueLED within the lead frame cup package.

These and other embodiments, features and advantages of the presentinvention will become more apparent to those skilled in the art whentaken with reference to the following more detailed description inconjunction with the accompanying drawings that are first brieflydescribed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the melanopic response curve.

FIG. 2 shows an embodiment of a lighting device with a maximized m/pratio and high color fidelity.

FIG. 3 shows a model spectrum of an embodiment of a lighting deviceaccording to the disclosure.

FIG. 4 shows another embodiment of a lighting device with a maximizedm/p ratio and high color fidelity.

FIG. 5 shows an embodiment of a lighting device according to thedisclosure formed in a single lead frame cup package.

FIG. 6 shows an embodiment of a tunable lighting system incorporatingthe lighting device disclosed herein.

FIG. 7 shows a tuning path in CIE 1976 color space of an example tunablelighting system incorporating the lighting device disclosed herein.

FIG. 8 shows primary spectra of an example tunable lighting systemincorporating the lighting device disclosed herein.

FIG. 9 shows color rendering indices Ra and R9 along the tuning path(CCT) of an example tunable lighting system incorporating the lightingdevice disclosed herein.

FIG. 10 shows the m/p ratio as a function of CCT for an example tunablelighting system incorporating the lighting device disclosed herein.

DETAILED DESCRIPTION

The following detailed description should be read with reference to thedrawings, in which identical reference numbers refer to like elementsthroughout the different figures. The drawings, which are notnecessarily to scale, depict selective embodiments and are not intendedto limit the scope of the invention. The detailed descriptionillustrates by way of example, not by way of limitation, the principlesof the invention.

The human circadian rhythm is a twenty-four hour cycle in the humanphysiological process and includes any biological process that displaysan endogenous and entrainable oscillation. Entrainment is theinteraction between circadian rhythms and the environment, such as theentrainment of circadian rhythms to the daily light-dark cycledetermined by the earth's rotation.

Light-induced circadian entrainment and other non-visual responses tolight are influenced by a photoreceptor as well as rod and conestructures in the eye. Together, these non-visual responses to light canproduce a day-like physiological state in the body.

Light-induced circadian entrainment generally has a peak spectralsensitivity in the short-wavelength end of the visual spectrum. Thisrange correlates with the action spectrum for melanopsin, which is thephotopigment in the eye expressed by the photoreceptor responsible forlight-induced circadian entrainment. FIG. 1 shows the melanopic responsecurve, which peaks at approximately 490 nm and has a full width at halfmaximum (FWHM) in the range of 447-531 nm including prereceptoralfiltering, as defined in CIE S026/E:2018.

In many lighting application, it is desirable to be able to vary themelanopic illuminance of the emitted spectrum using a tunable lightingsystem so as to provide conditions suitable for circadian entrainmentand to minimize circadian disruption. At a given photopic illuminance,the melanopic illuminance can be tuned by changing the correlated colortemperature (“CCT”) using conventional white LED spectra. Alternatively,the spectrum of the emitted light may be engineered to create either agap or a peak at the wavelength ranges coinciding with the melanopicpeak sensitivity. Such gaps and peaks may be referred to herein as a“cyan gap” or a “cyan peak.” To maximize the melanopic tuning range,both approaches may be combined, i.e. at one end of the tuning range,the spectrum may be cool-white with a cyan peak, while at the other endof the range, the spectrum may be warm-white with a cyan gap.

A useful metric to describe these spectra is the m/p ratio. The “m/pratio” is defined as the ratio of radiant flux weighted by the melanopicwavelength response (“m”) to the radiant flux weighted by photopicwavelength response (“p”), where the melanopic and photopic wavelengthresponses are normalized such that m/p=1 for an equal energy spectrum(“EES”). Using the m/p ratio normalizes the melanopic stimulation to thevisual (photopic) stimulation. Thus, a lighting system at a maximum m/pratio maximizes melanopic stimulation, while a lighting system at aminimum m/p ratio minimizes melanopic stimulation at a given retinalilluminance.

Conventional pcLEDs employing a royal-blue pump LED are not optimal foruse in tunable lighting systems which vary melanopic illuminance becausethe spectra required for such tunable lighting systems to have both amaximum tunable range of the m/p ratio and good color rendering cannotbe achieved. The emission peak wavelength of a pcLED employing aroyal-blue pump LED is 440-460 nm, which has significant overlap withthe melanopic sensitivity function (447-531 nm FWHM), prohibiting thedesign of a tunable lighting system that has a minimized m/p ratio. Theroyal-blue emission peak from the royal-blue pump LED is also notoptimal for the design of a tunable lighting system which has amaximized m/p ratio, as the royal-blue emission peak has a significantoffset in peak position relative to the melanopic sensitivity function.

Minimizing the m/p ratio may be achieved by the use of violet pump LEDs,which have a peak wavelength between 410-430 nm. Such violet pump LEDshave been proposed, and demonstrated (e.g. as disclosed in U.S. Pat. No.9,410,664) as a way to minimize m/p ratio while maintaining a (warm)white color point.

Maximizing the m/p ratio is more difficult. Shifting the pump LED tomatch the melanopic peak is not a practical solution as it reduces thecolor fidelity to values that are typically unacceptable. The use ofcyan phosphors to down-convert the royal-blue peak to match themelanopic sensitivity is also not practically possible because of thelack of efficient and reliable cyan phosphors with the desired narrowemission spectrum.

FIG. 2 shows an embodiment of a lighting device with a maximized m/pratio and high color fidelity. Lighting device 200 of FIG. 2 includes alight source 201 which is a combination of a royal-blue light source 203with a peak wavelength in the range of 435-460 nm and a blue lightsource 205 with a peak wavelength in the range of 470-495 nm.

Lighting device 200 of FIG. 2 also includes a wavelength convertingstructure 208 which includes a phosphor mixture containing at least onegreen phosphor and at least one red phosphor.

Light source 201 emits a first royal-blue light 204 from royal-bluelight source 203 and a first blue light 206 from blue light source 205.Portions of first royal-blue light 204 and first blue light 206 areincident upon wavelength converting structure 208. The green phosphorand red phosphor in the wavelength converting structure 208 absorb thefirst royal-blue light 204 and/or first blue light 206 and emit a secondlight 212. Second light 212 may include light down-converted by thegreen phosphors into the green spectral range (495-580 nm, whichincludes cyan, green and yellow) and light down-converted from the redphosphor into the red spectral range (580-660 nm, which includes amber,red-orange, red and deep red). Second light 212 may also include aportion of the first royal-blue light 204 and first blue light 206 whichis not down-converted. As used herein, a “green phosphor” is anymaterial capable of absorbing blue and/or royal-blue light, anddown-converting the absorbed light into light having a peak wavelengthwithin a green spectral range (495-580 nm). As used herein, a “redphosphor” is any material capable of absorbing blue and/or royal-bluelight and/or green light, and down converting the absorbed light intolight having a peak wavelength within a red spectral range (580-660 nm).Thus, in addition, or as an alternative, to absorbing a portion of thefirst royal-blue light 204 and/or first blue light 206, the red phosphormay absorb a portion of the light that has been down-converted from thegreen phosphor into the green spectral range, which the red phosphorthen down-converts into the red spectral range in second light 212.

FIG. 3 shows a model spectrum of an embodiment of a lighting device 200according to the disclosure. The model spectrum of FIG. 3 was generatedby mixing emission spectra of a royal-blue LED with peak wavelength of451 nm, a blue LED with peak wavelength of 475 nm, a green garnetphosphor and a red SCASN phosphor to a color point of u′=0.195 andv′=0.470. The ratio of unconverted blue radiant flux and unconvertedroyal-blue radiant flux used was 2.0. The spectrum shows a peak at 475nm, which is within the full width at half maximum (FWHM) range of447-531 of the melanopic response curve (FIG. 1). In general, thelighting device disclosed herein may have a peak within the range of447-531 nm, and more specifically may have a peak within the range of465-515 nm. The resulting device has a CCT of 6587K, a color renderingindex (“CRT”) Ra of 84, and an m/p ratio of 1.27.

In general a lighting device 200 according to the disclosure may have aCCT of 4000K or higher, or 5000K or higher. A lighting device 200according to the disclosure may have a CRT Ra>80. A lighting device 200according to the disclosure may have an m/p ratio that is greater thanthe m/p ratio of the CIE daylight illuminant with corresponding CCT.

Light sources 203 and 205 may be LEDs or any other suitable lightsources including, as examples, resonant cavity light emitting diodes(RCLEDs) and vertical cavity laser diodes (VCSELs). Light sources 203and 205 may be LED dies, for example III-nitride LEDs based on the InGaNmaterial system.

Phosphors used in phosphor converting structure 208 may be any suitablegreen phosphor and any suitable red phosphor.

Examples of green phosphors that may be used in converting structure 208include aluminum garnet phosphors with the general formula(Lu_(1−x−y−a−b)Y_(x)Gd_(y))₃(Al_(1−z)Ga_(z))₅O₁₂:Ce_(a)Pr_(b) wherein0<x<1, 0<y<, 0<z≤0.1, 0<a≤0.2 and 0<b≤0.1, such as Lu₃Al₅O₁₂:Ce³⁺ andY₃Al₅O₁₂:Ce³⁺ which emit light in the yellow-cyan range. Additionalexamples of suitable green phosphors include but are not limited toLu_(3−x−y)M_(y)Al_(5−z)A_(z)O₁₂:Ce_(x) where M=Y, Gd, Tb, Pr, Sm, Dy;A=Ga, Sc; and (0<x≤0.2); Ca_(3−x−y)M^(y)Sc_(2−z)A_(z)Si₃O₁₂:Ce_(x) whereM=Y, Lu; A=Mg, Ga; and (0<x≤0.2); Ba_(2−x−y)M_(y)SiO₄:Eu_(x) where M=Sr,Ca, Mg and (0<x≤0.2); Ba_(2−x−y−z)M_(y)K_(z)Si_(1−z)P_(z)O₄:Eu_(x) whereM=Sr, Ca, Mg and (0<x≤0.2);Sr_(1−x−y)M_(y)Al_(2−z)Si_(z)O_(4−z)N_(z):Eu_(x) where M=Ba, Ca, Mg and(0<x≤0.2); M_(1−x)Si₂O₂N₂:Eu_(x) where M=Sr, Ba, Ca, Mg and (0<x≤0.2);M_(3−x)Si₆O₉N₄:Eu_(x) where M=Sr, Ba, Ca, Mg and (0<x≤0.2);M_(3−x)Si₆O₁₂N₂:Eu_(x) where M=Sr, Ba, Ca, Mg and (0<x≤0.2);Sr_(1−x−y)M_(y)Ga_(2−z)Al_(z)S₄:Eu_(x) where M=Ba, Ca, Mg and (0<x≤0.2);Ca_(1−x−y−z)M_(z)S:Ce_(x)A_(y) where M=Ba, Sr, Mg; A=K, Na, Li; and(0<x≤0.2); Sr_(1−x−z)M_(z)Al_(1+y)Si_(4.2−y)N_(7−y)O_(0.4+y):Eu_(x)where M=Ba, Ca, Mg and (0<x≤0.2); Ca_(1−x−y−z)M_(y)Sc₂O₄:Ce_(x)A_(z)where M=Ba, Sr, Mg; Na, Li; and (0<x≤0.2);M_(x−z)Si_(6−y−2x)Al_(y+2x)O_(y)N_(8−y):Eu_(z) where M=Ca, Sr, Mg and(0<x≤0.2); and Ca_(8−x−y)M_(y)MgSiO₄Cl₂:Eu_(x) where M=Sr, Ba and(0<x≤0.2).

Examples of red phosphors that may be used in converting structure 208include (Sr_(1−x−y)Ba_(x)Ca_(y))_(2−z)Si_(5−a)Al_(a)N_(8−a)O_(a):Eu_(z)²⁺ wherein 0≤a<5, 0<x≤1, 0≤y≤1, and 0<z≤1, such as Sr₂Si₅N₈:Eu²⁺, whichemit light in the red range. Additional examples of suitable redemitting phosphors include Ca_(1−x−z)M_(z)S:Eu_(x) where M=Ba, Sr, Mg,Mn and (0<x≤0.2); Ca_(1−x−y)M_(y)Si¹⁻¹Al_(1+z)N_(3−z)O_(z):Eu_(x) whereM=Sr, Mg, Ce, Mn and (0<x≤0.2), Mg₄Ge_(1−x)O₅F:Mn_(x) where (0<x≤0.2);M_(2−x)Si_(5−y)Al_(y)N_(8−y)O_(y):Eu_(x) where M=Ba, Sr, Ca, Mg, Mn and(0<x≤0.2); Sr_(1−x−y)M_(y)Si_(4−z)Al_(1+z)N_(7−z)O_(z):Eu_(x) whereM=Ba, Ca, Mg, Mn and (0<x≤0.2); and Ca_(1−x−y)M_(y)SiN₂:Eu_(x) whereM=Ba, Sr, Mg, Mn and (0<x≤0.2).

Other cyan, yellow, and red emitting phosphors may also be suitable,including (Sr_(1−a−b)Ca_(b)Ba_(c))Si_(x)N_(y)O_(z):Eu_(a) ²⁺(a=0.002-0.2, b=0.0-0.25, c=0.0-0.25, x=1.5-2.5, y=1.5-2.5, z=1.5-2.5)including, for example, SrSi₂N₂O₂:Eu²⁺;(Sr_(1−u−v−x)Mg_(u)Ca_(v)Ba_(x))(Ga_(2−y−z)Al_(y)In_(z)S₄):Eu²⁺including, for example, SrGa₂S₄:Eu²⁺; Sr_(1−x)Ba_(x)SiO₄:Eu²⁺; and(Ca_(1−x)Sr_(x))S:Eu²⁺ wherein 0<x<1 including, for example, CaS:Eu²⁺and SrS:Eu²⁺.

In an example embodiment of lighting device 200, wavelength convertingstructure 208 may include the green phosphor(Lu_(1−x−y−a−b)Y_(x)Gd_(y))₃(Al_(1−z)Ga_(z))₅O₁₂:Ce_(a)Pr_(b) and thered phosphor is(S_(1−x−y)Ba_(x)Ca_(y))_(2−z)Si_(5−a)Al_(a)N_(8−a)O_(a):Eu_(z) ²⁺. Inthis particular example, the ratio of the amount of green phosphor tored phosphor may be approximately 21:1. In general, however, therelative amount of green phosphor and red phosphor used in wavelengthconverting structure 208 depends on many factors including, for example,the type of phosphor, the particle size and scattering cross-section ofthe phosphor particles, and any structure in the phosphor layers. Aperson of ordinary skill in the art would know the proportions of greenphosphor and red phosphor to include in the phosphor convertingstructure 208 to achieve a target white light.

FIG. 4 shows another embodiment of a lighting device with a maximizedm/p ratio and high color fidelity, and having increased unconvertedradiant flux of blue light relative to unconverted radiant flux ofroyal-blue light as compared to the embodiment disclosed in FIG. 2.

Lighting device 400 of FIG. 4 includes a light source 401 which is acombination of a royal-blue light source 403 with a peak wavelength inthe range of 435-460 nm and two blue light sources 405, 407, each with apeak wavelength in the range of 470-495 nm.

Lighting device 400 of FIG. 4 also includes a wavelength convertingstructure 408 which includes a phosphor mixture containing at least onegreen phosphor and at least one red phosphor.

Light source 401 emits a first royal-blue light 404 from royal-bluelight source 403 and a first blue light 406 from blue light sources 405,407. Portions of first royal-blue light 404 and first blue light 406 areincident upon wavelength converting structure 408. The wavelengthconverting structure 408 absorbs the first royal-blue light 404 andfirst blue light 406 and emits a second light 412. Second light 412 mayinclude light down-converted by the phosphors as well as a portion ofthe first royal-blue light 404 and first blue light 406 which is notdown-converted.

Because light source 401 includes two blue light sources, there is moreunconverted radiant flux of blue light than unconverted radiant flux ofroyal-blue light. When the amount of blue light is low relative toroyal-blue light, a lighting device as disclosed herein may not providethe desired normalized melanopic flux. Whereas when the amount of bluelight is high relative to the amount of royal-blue light, a lightingdevice as disclosed herein may not have enough royal-blue spectralcontent to meet color rendering criteria. There is some tolerance in therelative flux of the blue and royal-blue light, as the final color pointis determined partly by the phosphor mixture. The unconverted radiantflux of the blue light relative to the royal-blue light may be between0.7 and 2.8. Unconverted radiant flux may be difficult to measure in theemitted light (second light 412), therefore a more practical ratio isthe ratio of radiant flux of blue light having a wavelength range of 465to 495 nm to radiant flux of royal-blue light having a wavelength in therange of 435 to 465 nm in the second light 412 of the lighting device400, which ratio may be between 0.9 and 2.0.

FIG. 4 illustrates one method for adjusting the relative unconvertedradiant flux of blue vs. royal-blue light, by using an additional bluelight source. Alternatively (or additionally), the relative amount ofblue light to royal-blue light in the second light 212, 412 can beadjusted by, for example, driving the blue light source 206, 405, 407 ata higher drive current than the royal-blue light source 204, 403 or byusing a higher concentration of the green phosphor and/or red phosphorin an area of the wavelength converting structure 208, 408 positionedaround the royal-blue light source 204, 403 than in an area positionedaround the blue light source 206, 405, 407. A person having ordinaryskill in the art will understand that any suitable method to adjustrelative unconverted radiant flux of blue to royal-blue light may beused to achieve the ratio needed to provide maximum m/p whilemaintaining high color fidelity.

FIG. 5 shows an embodiment of a lighting device according to thedisclosure formed in a single lead frame cup package. Lighting device500 of FIG. 5 includes a blue LED die 502 and a royal-blue LED die 504in a single lead frame cup package 510. The green phosphor and redphosphor mixture are combined in a silicone slurry which is filled intothe cup package 510 over the blue LED die 502 and royal-blue LED die 504to form wavelength converting structure 508. In other embodiments, eachLED die may have its own phosphor mixture in wavelength convertingstructure 508, or wavelength converting structure 508 may cover only oneof the royal-blue and blue LED die.

In lighting device 500, the blue LED die 502 and royal-blue LED die 504are in a fixed electrical configuration such that the LED has a singlecathode and anode. Wires 520 connect the two LED dies 502, 504 in aseries configuration. In such a series configuration there is a singledrive current for both LED dies 502, 504, thus defining their relativepower, which is important for controlling the overall spectrum and colorpoint, as described above. The relative power may be changed by changingthe number of royal-blue LED dies and blue LED dies that are placed inseries. For example, the lead frame cup package may contain oneroyal-blue LED die and two blue LED dies.

In another embodiment, the royal-blue LED die and blue LED die may beelectrically connected in parallel. In a parallel configuration, therelative power is determined by the current at which the voltage of eachof the LED die types are in equilibrium.

FIG. 6 shows an embodiment of a tunable lighting system incorporatingthe lighting device disclosed herein. Tunable lighting system 600 ofFIG. 6 includes a first lighting device 601, which is a the cool-whitelighting device having a maximum m/p ratio, such as lighting devices 200and 400 as disclosed herein, and a second lighting device 603, which maybe a warm-white lighting device having a minimum m/p ratio, such as, forexample, the violet pumped LED disclosed in U.S. Pat. No. 9,410,664,incorporated herein by reference. In tunable lighting system 600, thefirst lighting device 601, which is a cool-white lighting device, mayhave an m/p ratio that is greater than a reference illuminant of thesame CCT; and the second lighting device 603, which is a warm-whitelighting device, may have an m/p ratio that is less than a referenceilluminant of the same CCT; where the reference illuminant may be ablackbody radiator or the CIE daylight illuminant. In one example, firstlighting device 601 may have an m/p ratio of 1.27 and second lightingdevice 603 may have an m/p ratio of 0.37.

Tunable lighting system 600 may be implemented at package level, forexample in a lead frame package with two cups, one for the cool-white,maximum m/p LED such as those disclosed herein, and one for thewarm-white, minimum m/p LED. Alternatively, tunable lighting system 600may be implemented at module level, with discrete LED packages for bothwarm-white, minimum m/p LED 603 and cool-white, maximum m/p LED 601.

The light emitted from the tunable lighting system 600 may be acombination of light emitted from the first lighting device 601 and thesecond lighting device 603, and the CCT and m/p ratio of the lightemitted from tunable lighting system 600 may be varied by varying theamount of light emitted by each lighting device. For example, when thefirst lighting device 601 is in an on state and the second lightingdevice 603 is in the off state, the emitted light may be a cool-whitelight having a maximum m/p ratio. When the first lighting device 601 inan off state and the second lighting device 603 is in an on state, thelight emitted may be a warm white having a minimum m/p ratio. When boththe first lighting device 601 and the second lighting device 603 are inthe on state, the light emitted from the lighting system 600 is amixture of the light emitted from the first lighting device 601 andsecond lighting device 603.

FIGS. 7, 8, 9 and 10 show results for an example embodiment of tunablelighting system 600, in which the warm-white, minimum m/p LED 603, suchas the violet-pumped LED, has a CCT of 2700K, and the cool-white,maximum m/p LED 601, such as those disclosed herein, has a CCT of 6500K.

FIG. 7 illustrates the tuning path in CIE 1976 color space of theexample embodiment of tunable lighting system 600. The exampleembodiment of tunable lighting system 600 enables the linear tuningrange between these two LEDs 601, 602 shown in FIG. 6. In FIG. 7, curve702 illustrates the Planckian locus between 2700K and 6500K and line 701shows the u′, v′ color of the tunable lighting system as the system istuned from the first lighting device to the second lighting device, andtargets 705 represent standard deviation color matching (SDCM) ellipses,also known as McAdam ellipses, around the center target. Thus, it can beseen from FIG. 7, that tunable lighting system 600 tunes between thewarm-white and cool-white color.

FIG. 8 shows the modeled primary spectra for the example embodiment oftunable lighting system 600. Spectrum 810 is from the cool-white,maximum m/p LED as disclosed herein, and Spectrum 820 is from thewarm-white, minimum m/p LED. FIG. 8 shows the cyan peak 813 of thecool-white, maximum m/p LED spectrum 820. For comparison, the melanopicresponse curve 830 is also shown. As can be seen in FIG. 8, the cyanpeak 813 of the cool-white, maximum m/p LED is at a wavelength of 475 nmand overlaps with the peak of the melanopic response curve 830.

FIG. 9 shows the calculated color rendering indices Ra and R9 along thetuning path (CCT) for the example embodiment of tunable lighting system600. CRI indices were calculated from the spectral power distribution(CIE 13.3-1995), as understood by persons having ordinary skill in theart. R9 represents the strong red color and is often specifiedseparately because red rendering is an important factor for subjectivepreference. The color rendering index Ra along the tuning path (curve910) stays greater than 80 for all CCT (2700K to 6500K), and the colorrendering index R9 along the tuning path (curve 920) stays greater than65. Thus, an Ra>80 and R9>50 can be easily maintained.

FIG. 10 shows the m/p ratio as a function of CCT 910 for the exampleembodiment of tunable lighting system 600. Curves for a referenceilluminant (Planckian radiator below 5000K and the daylight illuminantdefined by the CIE D series above 5000K) 1020 and state of the arttunable systems based on standard CRI 80 1030 and CRI 90 1040 LEDs arealso included. As shown in this comparison, this tunable lighting systemusing the cool-white, maximum m/p lighting device disclosed hereinsignificantly widens the range in m/p ratio that is realized with CCTtuning. In particular, the m/p ratio values range from 0.37 when tunablelighting system 600 is at CCT 2700K to 1.27 when tunable lighting system600 is at CCT 6500K. The m/p ratio values from FIG. 10 are alsosummarized in Table 1, below for comparison.

TABLE 1 Summary of normalized melanopic range of CCT tuning systemsshown in FIG. 10. m/p ratio Low (2700K) High (6500K) Referenceilluminant 0.51 1.10 LED: high melanopic range of 0.37 1.27 tunablelighting system 600 LED: standard CRI 80 0.47 0.92 LED: standard CRI 900.48 1.03

This disclosure is illustrative and not limiting. Further modificationswill be apparent to one skilled in the art in light of this disclosureand are intended to fall within the scope of the appended claims.

What is claimed is:
 1. A lighting device comprising: a light source, thelight source including a royal-blue light source configured to emit aroyal-blue light with a peak wavelength between 435-460 nm and a bluelight source configured to emit light with a peak wavelength between470-496 nm; a wavelength converting structure disposed in a path of theroyal-blue light and the blue light, the wavelength converting structureincluding: a green phosphor, the green phosphor configured to absorb afirst portion of at least one of the royal-blue light and the bluelight, and to down-covert the first portion to green light; and a redphosphor configured to absorb at least one of a second portion of atleast one of the royal-blue light and the blue light and a portion ofthe green light, and to down-convert the at least one of the secondportion and the portion of the green light to red light; the wavelengthconverting structure configured to emit a second light, the second lightincluding the green light, the red light, an unconverted portion of theroyal-blue light, and an unconverted portion of the blue light thesecond light having a spectrum with a maximum spectral power densitybetween 465 and 515 nm.
 2. The lighting device of claim 1, furthercomprising a second blue light source configured to emit light with apeak wavelength range between 470-496 nm.
 3. The lighting device ofclaim 2, wherein a ratio of radiant flux of blue light havingwavelengths in the range of 465-495 nm to radiant flux of royal-bluelight having wavelengths in the range of 435-465 nm in the second lightis between 2.0 and 2.8.
 4. The lighting device of claim 1, wherein theroyal-blue light source is a royal-blue LED and the blue light source isa blue LED.
 5. The lighting device of claim 4, further comprising a leadframe cup package, the royal-blue LED and blue LED being both mountedinside the lead frame cup package, the wavelength converting structurebeing disposed over the royal-blue LED and blue LED within the leadframe cup package.
 6. The lighting device of claim 5, wherein theroyal-blue LED and the blue LED are electrically connected in series. 7.The lighting device of claim 1, wherein the royal-blue LED and the blueLED are electrically connected in parallel.
 8. The lighting device ofclaim 1, wherein an m/p ratio of the second light is greater than an m/pratio of the CIE daylight illuminant at a corresponding CCT value. 9.The lighting device of claim 1, wherein a CCT value of the second lightis 4000K or greater and a color rendering index of the second light hasan Ra value greater than
 80. 10. A tunable lighting system comprising: afirst lighting device configured to emit a first light, the first lighthaving a first m/p ratio; and a second lighting device configured toemit a second light, the second light having a second m/p ratio that issmaller than the first m/p ratio, the tunable lighting system beingconfigured to emit a third light, the third light including at least oneof the first light, the second light, or a combination of the firstlight and the second light, the first lighting device comprising: alight source, the light source including a royal-blue light sourceconfigured to emit a royal-blue light with a peak wavelength between435-460 nm and a blue light source configured to emit light with a peakwavelength between 470-496 nm; and a wavelength converting structuredisposed in a path of the royal-blue light and the blue light, thewavelength converting structure including a mixture of a green phosphorand a red phosphor, the green phosphor configured to absorb a firstportion of at least one of the royal-blue light and the blue light, andto down-covert the first portion to green light; and the red phosphorconfigured to absorb at least one of a second portion of at least one ofthe royal-blue light and the blue light and a portion of the greenlight, and to down-convert at least one of the second portion and theportion of green light to red light; the wavelength converting structurebeing configured to emit the first light, the first light including thegreen light, the red light, an unconverted portion of the royal-bluelight, and an unconverted portion of the blue light.
 11. The tunablelighting system of claim 10, wherein the royal-blue light source is aroyal-blue LED, the blue light source is a blue LED, and the secondlighting device is a violet pumped LED.
 12. The tunable lighting systemof claim 11, wherein the first lighting device further comprises a leadframe cup package, the royal-blue LED and blue LED both being mountedinside the lead frame cup package, the wavelength converting structuredisposed over the royal-blue LED and blue LED within the lead frame cuppackage.
 13. The tunable lighting system of claim 10, wherein a CCTvalue of the third light is between 2700K and 6500K, and an m/p ratio ofthe third light is between 0.37 and 1.27.
 14. The tunable lightingsystem of claim 10, wherein a color rendering index Ra value of thethird light is greater than 80, and a color rendering index R9 value ofthe third light is greater than
 50. 15. The tunable lighting system ofclaim 10, wherein the first light has a maximum spectral power densitybetween 465 and 515 nm, and the second light has a minimum spectralpower density between 447 nm and 531 nm.
 16. The tunable lighting systemof claim 10, wherein the red phosphor comprises at least one of(Sr_(1−x−y)Ba_(x)Ca_(y))_(2−z)Si_(5−a)Al_(a)N_(8−a)O_(a):Eu_(z) ²⁺ where0≤a<5, 0<x≤1, 0≤y≤1, and 0<z≤1, Ca_(1−x−z)M_(z)S:Eu_(x) where M=Ba, Sr,Mg, Mn and (0<x≤0.2); Ca_(1−x−y)M_(y)Si¹⁻¹Al_(1+z)N_(3−z)O_(z):Eu_(x)where M=Sr, Mg, Ce, Mn and (0<x≤0.2), Mg₄Ge_(1−x)O₅F:Mn_(x) where(0<x≤0.2); M_(2−x)Si_(5−y)Al_(y)N_(8−y)O_(y):Eu_(x) where M=Ba, Sr, Ca,Mg, Mn and (0<x≤0.2); Sr_(1−x−y)M_(y)Si_(4−z)Al_(1+z)N_(7−z)O_(z):Eu_(x)where M=Ba, Ca, Mg, Mn and (0<x≤0.2); and Ca_(1−x−y)M_(y)SiN₂:Eu_(x)where M=Ba, Sr, Mg, Mn and (0<x≤0.2).
 17. The tunable lighting system ofclaim 10, wherein the green phosphor comprises at least one of(Lu_(1−x−y−a−b)Y_(x)Gd_(y))₃(Al_(1−z)Ga_(z))₅O₁₂:Ce_(a)Pr_(b) where0<x<1, 0<y<, 0<z≤0.1, 0<a≤0.2 and 0<b≤0.1,Lu_(3−x−y)M_(y)Al_(5−z)A_(z)O₁₂:Ce_(x) where M=Y, Gd, Tb, Pr, Sm, Dy;A=Ga, Sc; and (0<x≤0.2); Ca_(3−x−y)M^(y)Sc_(2−z)A_(z)Si₃O₁₂:Ce_(x) whereM=Y, Lu; A=Mg, Ga; and (0<x≤0.2); Ba_(2−x−y)M_(y)SiO₄:Eu_(x) where M=Sr,Ca, Mg and (0<x≤0.2); Ba_(2−x−y−z)M_(y)K_(z)Si_(1−z)P_(z)O₄:Eu_(x) whereM=Sr, Ca, Mg and (0<x≤0.2);Sr_(1−x−y)M_(y)Al_(2−z)Si_(z)O_(4−z)N_(z):Eu_(x) where M=Ba, Ca, Mg and(0<x≤0.2); M_(1−x)Si₂O₂N₂:Eu_(x) where M=Sr, Ba, Ca, Mg and (0<x≤0.2);M_(3−x)Si₆O₉N₄:Eu_(x) where M=Sr, Ba, Ca, Mg and (0<x≤0.2);M_(3−x)Si₆O₁₂N₂:Eu_(x) where M=Sr, Ba, Ca, Mg and (0<x≤0.2);Sr_(1−x−y)M_(y)Ga_(2−z)Al_(z)S₄:Eu_(x) where M=Ba, Ca, Mg and (0<x≤0.2);Ca_(1−x−y−z)M_(z)S:Ce_(x)A_(y) where M=Ba, Sr, Mg; A=K, Na, Li; and(0<x≤0.2); Sr_(1−x−z)M_(z)Al_(1+y)Si_(4.2−y)N_(7−y)O_(0.4+y):Eu_(x)where M=Ba, Ca, Mg and (0<x≤0.2); Ca_(1−x−y−z)M_(y)Sc₂O₄:Ce_(x)A_(z)where M=Ba, Sr, Mg; Na, Li; and (0<x≤0.2);M_(x−z)Si_(6−y−2x)Al_(y+2x)O_(y)N_(8−y):Eu_(z) where M=Ca, Sr, Mg and(0<x≤0.2); and Ca_(8−x−y)M_(y)MgSiO₄Cl₂:Eu_(x) where M=Sr, Ba and(0<x≤0.2).
 18. The tunable lighting system of claim 10, wherein thegreen phosphor is(Lu_(1−x−y−a−b)Y_(x)Gd_(y))₃(Al_(1−z)Ga_(z))₅O₁₂:Ce_(a)Pr_(b) and thered phosphor is(Sr_(1−x−y)Ba_(x)Ca_(y))_(2−z)Si_(5−a)Al_(a)N_(8−a)O_(a):Eu_(z) ²⁺ and aratio of the amount of green phosphor to red phosphor is approximately21:1.
 19. The tunable lighting system of claim 10, wherein the first m/pratio is below the m/p ratio of the CIE daylight illuminant at CCTvalues below 3000K, and the second m/p ratio is above the m/p ratio ofthe CIE daylight illuminant at CCT values above 6500K.